Sony intent on having swappabale themes worked with google to devise the current implementation of rro that provides a much more secure way of going about it.
They modified the asset manager to accept apks with just resources and map out the id of each resource in android and then overlay the modified resources at just runtime so those resources can map out to rro's changed or new resources to act like they were always part of those resources but only as long as that apk is there and loaded into the system.
With this system, it provides security because the system is already given permission but still confined in all of android but it is also powerful because new resources can made to add features, translations and so forth very quickly (OEMS are actually using it now to prototype )
With this system in place, the code was merged into aosp for lollipop, unfortunately with google keeping lollipop source mostly hidden, nobody realized that it broke in the process until 5.0 was already out and Sony quickly patched it in aosp for the next release (the 5 commits that need to be cherry picked for rro to properly work)
This means that future stock builds of android has this native theme engine built into it and Sony and Samsung and HTC are actually already using it (rumor is this works already in gpe Sony and Samsung lollipop builds) so it makes sense for the community to embrace it and build on it as our own project.
Cm though decided instead of embracing RRO (maybe they didn't know about it) ported their legacy code up for the theme engine with so much effort instead of looking for a new way with 13,000+ lines of code instead of probably about 200 lines of code to adapt the theme engine into was was already there so there is a ton of redundant code that is completely ridiculous.